On Friday, 14 March 2014 at 14:48:13 UTC, Steven Schveighoffer
wrote:
On Thu, 13 Mar 2014 11:24:01 -0400, Steven Schveighoffer
<schvei...@yahoo.com> wrote:
arr.length = 0;
...
3. Don's company uses D1 as its language, I highly recommend
watching Don's Dconf13 presentation (and look forward to his
Dconf14 one!) to see how effective D code can create
unbelievable speed, especially where array slices are
concerned. But to the above line, in D2, they must add the
following code to get the same behavior:
arr.assumeSafeAppend();
Just a quick note, buried in same thread that Don mentioned, he
outlined a more specific case, and this does not involve
setting length to 0, but to any arbitrary value.
This means my approach does not help them, and although it
makes sense, the idea that it would help Sociomantic move to D2
is not correct.
-Steve
Actually it would help a great deal. In most cases, we do set the
length to 0. That example code is unusual.
FYI: In D1, this was the most important idiom in the language.
In the first D conference in 2007, a feature T[new] was
described, specifically to support this idiom in a safe manner.
Implementation was begun in the compiler. Unfortunately, it
didn't happen in the end. I'm not sure if it would actually have
worked or not.
BTW you said somewhere that concatenation always allocates. What
I actually meant was ~=, not ~. In our code it is always preceded
by .length = 0 though.
It's important that ~= should not allocate, when the existing
capacity is large enough.
